United are expected to sign Greenwood ahead of the new season. Greenwood, 16, is an England Under-16 international.
Greenwood is regarded as one of the best young talents in his age range.
He scored 21 goals in 26 games across Sunderland's U16s and U18s last season and his performances for club and country have brought him to the attention of Europe's elite after he turned down a new deal at Sunderland.
Arsenal are also being linked with the teen.